Question

A quality of aluminium has a mass of $54g$. What is the mass of the same number of magnesium?
A.$12.1g$
B.$24.3g$
C.$48.6g$
D.$97.2g$

Answer 1

To find the mass of magnesium we first need to find the number of moles of aluminium by calculating moles of a material you have, divide the mass of the material by its molar mass. The molar mass of a substance is the mass in grams of one mole of that substance. And then calculate the mass of magnesium by multiplying the number of moles with the molecular mass of magnesium.

Complete answer:
The mole is a measure or the base unit for the amount of substance present in the given sample. $1$ mole is a number which is equal to $6.022 \times {10^{23}}$ particles, also known as the Avogadro's constant. These particles can be any type of species, for example atoms, molecules, electrons, protons, neutrons etc.
The formula for the number of moles formula is expressed as
$\Rightarrow$ number of moles $= \dfrac{{mass\;of\;substance}}{{mass\;of\;1mole}}$
Weight of aluminium$= 54g$
Moles of aluminium$= \dfrac{{54}}{{27}}$
$\Rightarrow 2$
Number of moles of magnesium is also $2$
To find the mass of magnesium Multiply the number of moles of the magnesium by its molar mass in $\dfrac{{grams}}{{mole}}$.
Mass of magnesium ion becomes
$\Rightarrow$Moles $\times$ $24$
$\Rightarrow 48g$
So, the correct answer is C i.e $48.6g$

Note:
The molar mass of a substance depends not only on its molecular formula, but also on the distribution of isotopes of each chemical element present in it. For example, the mass of one mole of calcium $- 40$ is $39.9 \pm 0,00000027$ grams, whereas the mass of one mole of calcium $- 42$ is $41.95 \pm 0.00000027$ grams, and of one mole of calcium with the normal isotopic mix is $40.078 \pm 0.004$ grams.